CN111757228A

CN111757228A - MEMS microphone

Info

Publication number: CN111757228A
Application number: CN202010642539.2A
Authority: CN
Inventors: 赵转转; 柏杨; 但强; 王凯杰; 李杨; 张睿
Original assignee: Ruisheng Technology Nanjing Co Ltd
Current assignee: AAC Technologies Holdings Nanjing Co Ltd; Ruisheng Technology Nanjing Co Ltd
Priority date: 2020-07-06
Filing date: 2020-07-06
Publication date: 2020-10-09
Also published as: WO2022007000A1

Abstract

The invention provides an MEMS microphone, which comprises a base with a back cavity, a vibrating diaphragm arranged at an interval with the base, and a back plate covering the vibrating diaphragm and having an inner cavity with the vibrating diaphragm at an interval; the back plate has at least one protrusion rising in a direction away from the diaphragm. The existence of bellying has increased the distance of backplate with the vibrating diaphragm, and after the sound wave air current got into the inner chamber through the acoustics hole, the velocity of flow of sound wave air current in the inner chamber that the bellying corresponds was less than the average airflow velocity of flow of inner chamber to reduce the press mold damping, and then reduced MEMS microphone's mechanical noise.

Description

MEMS microphone

[ technical field ] A method for producing a semiconductor device

The invention relates to the technical field of acoustics, in particular to an MEMS (micro-electromechanical system) microphone.

[ background of the invention ]

In a MEMS (Micro Electro mechanical System) microphone in the prior art, a vibrating diaphragm is disposed on a base at intervals, and a back plate is disposed above the vibrating diaphragm at intervals in an inner cavity. The vibrating diaphragm and the back plate are parallel to each other, and a flat capacitor system is formed. When sound wave airflow enters an inner cavity between the back plate and the vibrating diaphragm, sound pressure acts on the vibrating diaphragm to cause the vibrating diaphragm to move, the distance between the film and the back plate is changed through the movement, then the capacitor is changed, the capacitor is finally converted into an electric signal, and finally the corresponding function of the microphone is achieved. However, because the cavity between the diaphragm and the backplate is small, the air flow near the edges of the diaphragm and backplate when air flows is less than the air flow in the central region of the cavity, i.e., squeeze film damping exists when air flows between the diaphragm and the backplate. The squeeze film damping has a great influence on the dynamic response of the MEMS chip, and the larger the damping is, the larger the mechanical noise is.

Therefore, it is necessary to provide a MEMS microphone to solve the problem of large damping of the piezoelectric film in the MEMS chip.

[ summary of the invention ]

The invention aims to provide a MEMS microphone capable of reducing mechanical noise.

The technical scheme of the invention is as follows: an MEMS microphone comprises a base with a back cavity, a vibrating diaphragm arranged at an interval with the base, and a back plate covering the vibrating diaphragm and having an inner cavity with the vibrating diaphragm at an interval; the back plate has at least one protrusion rising in a direction away from the diaphragm.

Preferably, the at least one protrusion includes a first protrusion, the backplate includes a fixing portion and a main body portion surrounded by and connected to the fixing portion, and the fixing portion protrudes in a direction away from the diaphragm to form the first protrusion.

More preferably, the first protrusion is located at an outer periphery of the fixing portion.

More preferably, the first protruding portion is spaced from an outer periphery of the fixing portion.

Preferably, the at least one protrusion further includes a second protrusion, and the main body portion of the backplate is protruded in a direction away from the diaphragm to form the second protrusion.

Preferably, the distance from the main body portion to the diaphragm decreases gradually from the central position of the main body portion to the fixing portion.

Preferably, the main body of the back plate is provided with an acoustic hole communicating the inner cavity and the external environment.

Preferably, a first insulating layer is arranged between the diaphragm and the back plate, and the fixing portion is fixedly connected with the first insulating layer.

Preferably, a second insulating layer and a plurality of etching barrier walls are arranged between the diaphragm and the base.

The invention has the beneficial effects that: the back plate has at least one bulge portion bulging in a direction away from the diaphragm, so that the distance between the position of the back plate with the bulge portion and the diaphragm is larger than the average distance between the back plate and the diaphragm. The design ensures that the air flow velocity of the inner cavity corresponding to the bulge part is less than the average flow velocity of the air flow in the inner cavity, thereby reducing the squeeze film damping in the inner cavity and reducing the mechanical noise of the MEMS chip.

[ description of the drawings ]

Fig. 1 is a cross-sectional view of a MEMS microphone according to a first embodiment of the invention;

fig. 2 is a cross-sectional view of a MEMS microphone according to a second embodiment of the invention;

fig. 3 is a cross-sectional view of a MEMS microphone according to a third embodiment of the invention;

fig. 4 is a cross-sectional view of a MEMS microphone according to a fourth embodiment of the invention.

[ detailed description ] embodiments

The invention is further described with reference to the following figures and embodiments.

Referring to fig. 1, in a first embodiment of the present invention, the MEMS microphone includes a base 1 having a back cavity 11, and a diaphragm 2 and a back plate 4 sequentially disposed on a surface of the base 1.

The back plate 4 comprises a fixing portion 46 and a main body portion 45 surrounded by and connected to the fixing portion 46, the fixing portion 46 of the back plate being an edge of the back plate 4, wherein the main body portion 45 is disposed at intervals. A first insulating layer 6 is arranged between the back plate 4 and the diaphragm 2, so that the back plate 4 is isolated from the diaphragm 2, and the fixing portion 46 is fixedly connected with the first insulating layer 6.

A second insulating layer 21 is arranged between the diaphragm 2 and the base 1, thereby isolating the diaphragm 2 from the base 1, and the first insulating layer 6 at least partially covers the second insulating layer 21. The edge of the diaphragm 2 is connected with the base 1 through the second insulating layer 21, only the edge end of the diaphragm 2 is connected with the second insulating layer 21, and the position where the diaphragm 2 is not fixedly connected with the second insulating layer 21 can vibrate freely, that is, the central area of the diaphragm 2 can vibrate freely, so that the vibration effect of the diaphragm 2 is maintained. Since the second insulating layer 21 is disposed between the diaphragm 2 and the base 1, the diaphragm 2 and the base 1 are spaced apart to form a gap. The displacement space in which the diaphragm 2 vibrates is increased.

An inner cavity 3 is formed between the back plate 4 (i.e., the body portion 45) and the diaphragm 2, and a capacitor is present in the inner cavity 3. When the vibrating diaphragm 2 vibrates, the height of the inner cavity 3 in the direction perpendicular to the vibrating diaphragm 2 is changed, the capacitance value of the inner cavity 3 is further changed, the change of the capacitance is converted into a digital signal, and finally the function of the microphone is achieved.

In a modified embodiment, a plurality of etching barrier walls 5 may be further disposed between the diaphragm 2 and the base 1, and the etching barrier walls 5 may ensure a reliable stop of an etching process that may occur in a manufacturing process, thereby protecting the second insulating layer 21 from being etched away. The etching barrier walls 5 are arranged at intervals, and a second insulating layer 21 is arranged between every two etching barrier walls 5. The second insulating layer 21 and the etching barrier wall 5 support the diaphragm 2 together, so that the diaphragm 2 and the base 1 form a gap at intervals. The etch barrier 5 may typically be made of, for example, oxide, thermal oxide, or TEOS. Its thickness may be between 0.1 and 1 μm.

At a position where the body portion 45 is close to the fixing portion 46 and is spaced apart from the outer peripheral edge of the fixing portion 46, a first bulging portion 41 bulging in a direction away from the diaphragm 2 is provided, and the first bulging portion 41 has a higher height at a corresponding position in the cavity 3, so that the distance between the backplate 4 and the diaphragm 2 at the first bulging portion 41 is increased. When the sound wave airflow enters the inner cavity 3 through the acoustic holes 42, the airflow can enter the lower part of the raised first protruding part 41 at the edge of the inner cavity 3, so that the air in the inner cavity 3 is not compressed, the squeeze film damping in the inner cavity 3 is reduced, and the mechanical noise of the MEMS microphone is reduced.

Preferably, the back plate 4 is provided with acoustic holes 42 at regular intervals, the acoustic holes 42 communicate the inner cavity 3 with the external environment, the acoustic holes 42 are small through holes, so that the sound wave airflow can enter or exit the inner cavity 3, the acoustic holes 42 are uniformly distributed on the back plate 4, and when the sound wave airflow is transmitted to the MEMS microphone, the sound wave airflow passes through the acoustic holes 42 and enters the inner cavity 3. Overall, the whole back plate 4 is like a net with dense and hemp pores arranged in the middle.

Referring to fig. 1, the cross section of the back cavity 11 is an inverted isosceles trapezoid. The back cavity 11 has atmospheric pressure, and when the diaphragm 2 vibrates, the pressure in the back cavity 11 is constant, so that the free vibration of the diaphragm 2 is maintained.

With reference to fig. 1, the cross section of the first protruding portion 41 is similar to an isosceles triangle, and a similar sun hat or isosceles triangle structure is used to enhance the structural strength of the first protruding portion 41, so that the first protruding portion 41 is not easily deformed.

As shown in fig. 2, in the second embodiment of the present invention, the first protrusion 41' is provided at the position of the outer periphery of the fixing portion 46 of the backplate 4, and protrudes from the backplate fixing portion 46 in the direction away from the diaphragm 2. The position of the first protruding portion 41 'is changed compared with the first embodiment, but the first protruding portion 41 of the first embodiment and the first protruding portion 41' of the second embodiment both function to increase the height space in which the edge position of the cavity 3 is in the direction perpendicular to the diaphragm 2. After the sound wave airflow enters the inner cavity 3 through the acoustic holes 42, the sound wave airflow flows in the inner cavity 3, and due to the arrangement of the first protruding parts (41, 41'), the height space of the edge of the inner cavity 3 in the direction perpendicular to the vibrating diaphragm 2 is increased, and the sound wave airflow does not form air compression at the edge of the inner cavity 3 any longer, so that the squeeze film damping at the edge of the inner cavity 3 is reduced. The mechanical noise of the MEMS microphone is reduced after the squeeze film damping in the cavity 3 is reduced.

More preferably, referring to fig. 3, based on the first embodiment, a second protrusion 43 is further disposed in a central region of the main body portion 45, the second protrusion 43 protrudes away from the diaphragm 2, and a central axis of the second protrusion 43 coincides with a central axis of the main body portion 45 and the diaphragm 2. The second convex portion 43 extends from the bottom of the first convex portion 41 to the central axis direction of the main body portion 45, and gradually rises to form the second convex portion 43, and the center of the main body portion 45 is the peak of the second convex portion 43. More specifically, the second protrusion 43 is formed by raising the middle of the main body 45, and the distance from the main body 45 to the diaphragm 2 decreases gradually from the center of the main body 45 toward the fixing portion 46. The second raised portion 43 makes the height of the central region of the cavity 3 in a direction perpendicular to the diaphragm 2 greater than the average height of the cavity 3. When the acoustic airflow enters the inner cavity 3 through the acoustic holes 42, the flow velocity of the airflow in the central region of the inner cavity 3 is not greater than the average flow velocity in the inner cavity 3, thereby reducing squeeze film damping in the inner cavity 3.

Specifically, referring to fig. 3, the second protrusion 43 is in the shape of a circular arc and is formed to protrude from the central region of the main body 45 in a direction away from the diaphragm 2; the backplate fixing portion 46 is fixedly connected to the first insulating layer 6, and since the second boss portion 43 has an arch bridge shape in cross section, the central portion of the main body portion 45 is supported by the arch bridge shape and does not collapse downward, so that a large distance is maintained between the central region of the main body portion 45 and the diaphragm 2. The height of the central area of the inner cavity 3 is larger than the average height of the inner cavity 3, and when the sound wave airflow flows in the inner cavity 3, the airflow velocity of the central area of the inner cavity 3 is minimum, so that the squeeze film damping of the central area of the inner cavity 3 is reduced.

Referring to fig. 4, based on the second embodiment, a second convex portion 43 is also provided in the central region of the main body portion 45. The second protrusion portion 43 is disposed in a central region of the main body portion 45, the second protrusion portion 43 extends from the central region toward an edge of the back plate 4 and gradually decreases in height of the ridge, and the edge of the second protrusion portion 43 is connected to a hypotenuse of the first protrusion portion 41'. The protrusions are arranged in the central area of the back plate 4 and the fixing portion 46, so that the space size of the inner cavity 3 can be improved, and the squeeze film damping in the inner cavity 3 is reduced.

While the foregoing is directed to embodiments of the present invention, it will be understood by those skilled in the art that various changes may be made without departing from the spirit and scope of the invention.

Claims

1. An MEMS microphone comprises a base with a back cavity, a vibrating diaphragm arranged at an interval with the base, and a back plate covering the vibrating diaphragm and having an inner cavity with the vibrating diaphragm at an interval; the back plate is characterized by having at least one bulge part bulging towards the direction far away from the diaphragm.

2. The MEMS microphone of claim 1, wherein the at least one protrusion comprises a first protrusion, the backplate comprises a fixed portion and a body portion surrounded by and connected to the fixed portion, and the fixed portion bulges away from the diaphragm to form the first protrusion.

3. The MEMS microphone of claim 2, wherein the first protrusion is located at an outer periphery of the retainer.

4. The MEMS microphone of claim 2, wherein the first raised portion is spaced from an outer periphery of the retainer portion.

5. The MEMS microphone of claim 2, wherein the at least one raised portion further comprises a second raised portion, the body portion of the backplate bulging away from the diaphragm to form the second raised portion.

6. The MEMS microphone of claim 5, wherein the distance from the main body portion to the diaphragm decreases gradually from the center of the main body portion toward the fixing portion.

7. The MEMS microphone of claim 6, wherein the main body portion of the backplate is provided with an acoustic hole communicating the internal cavity with the external environment.

8. The MEMS microphone of claim 1, wherein a first insulating layer is disposed between the diaphragm and the backplate, and the fixing portion is fixedly connected to the first insulating layer.

9. The MEMS microphone of claim 1, wherein a second insulating layer and a plurality of etching barrier walls are disposed between the diaphragm and the base.